Metropolitan Transportation Authority (MTA) Montague and Greenpoint tunnels heavily damaged by Superstorm Sandy will require extended work to repair and rebuild their vital systems in order to ensure rider safety and reliable service. Both tunnels will be closed to subway traffic while work is completed.

The Greenpoint Tube, which carries the G train under Newtown Creek between Brooklyn and Queens, will be closed for 12, 53-hour long weekends this summer and fall starting July 6. The closures, which are subject to change, are planned to start at midnight on each Friday of the following weekends: July 6-7, 13-14, 20-21; August 3-4, 10-11, 17-18, 24-25; September 7-8, 28-29; October 5-6; December 7-8, and 14-15. Additionally, there will be a five-week 24/7 Greenpoint Tube closure in summer 2014.

By shutting down the Greenpoint Tube for12 weekends this year, the damaged systems can be repaired in a shorter amount of time during periods of lighter ridership. The northernmost three stops, Greenpoint Ave., 21st Street and Court Square, will be closed, affecting 32,000 Saturday and 25,000 Sunday customers. G trains will still operate to and from Church Ave. and Nassau Ave.

The Montague Tube, an almost mile-long pair of tunnels that carries the R train under the East River between Brooklyn and Manhattan, will be closed for up to 14 months starting the first week in August.

"Closing these two subway tubes is a difficult but necessary step to restore them to the condition they were in before Sandy struck," said MTA Acting Chairman Fernando Ferrer. "The temporary repairs that returned these tubes to operation after Sandy are not enough to provide reliable service. This is unfortunately the reality of recovery from Sandy: the damage is insidious and continuing and repairing it will take billions of dollars over several years."

"Even after we restored service through the tubes again, signal and other component failures rose dramatically," said Thomas Prendergast, MTA interim executive director. "The chief area of concern is the tubes' mechanical and electrical systems that were subjected to salt water, accelerating the deterioration of these vital systems and reducing their reliability over time."

Sandy inundated the tubes with millions of gallons of seawater, which corroded, degraded or ruined almost everything from tracks and switches, to signals and controls, to power and communications cables. Temporary fixes brought those tunnels back into service, but the damage has led to increased failures of components, a growing number of delayed trains and a pressing need to make permanent repairs.

In the Greenpoint Tube, power cables that were immersed in salt water are corroding from the inside, while corrosion on the outside of rails and fasteners raises the potential for short circuits. The controls for ventilation, lighting and communication systems were destroyed and have not been restored to their pre-Sandy condition.

The Montague Tube is in far worse condition and will require much more extensive repairs. It was flooded for a length of 4,025 feet to a depth of 20 feet with corrosive salt water sitting stagnant in the tube for 10 days. More than 27 million gallons of water were eventually pumped from the tube before work began to make it useable again for train service. While the work was enough to restore R service between Brooklyn Heights and Lower Manhattan, it was never intended to be a permanent repair.

Concrete and terra cotta duct banks under the walkways along the sides of the Montague tunnels, built in 1920, were compromised while underwater for weeks and collapsed in many areas. That left cables exposed and unprotected, but the extensive damage makes it impossible to simply pull new cables through the ducts. The duct banks must be removed and rebuilt, making them available to be used as emergency exits from trains.

In the Montague Tube, the necessary work is so extensive that performing repairs only on nights and weekends would extend into 2016 to complete, delaying its return to reliable service and the ability to perform work on adjacent subway lines which also require rehabilitation from Sandy damage.